WASHINGTON – As angry truckers encircled the Capitol in a horn-blaring caravan and consumers across the country agonized over $60 fill-ups, the issue of high fuel prices flared on the campaign trail Monday, sharply dividing the two Democratic candidates.

Sen. Hillary Clinton lined up with Sen. John McCain, the presumptive Republican nominee for president, in endorsing a plan to suspend the federal excise tax on gasoline of 18.4 cents a gallon for the summer travel season. But Sen. Barack Obama, Clinton’s Democratic rival, spoke out firmly against the proposal, saying it would save consumers little and do nothing to curtail oil consumption and imports.

While Obama’s view is shared by environmentalists and many independent energy analysts, his position allowed Clinton to draw a contrast with her opponent in appealing to the hard-hit middle-class families and older Americans who have proven to be the bedrock of her support. She has accused Obama of being out of touch with ordinary Americans who are struggling to meet their mortgages and gas up their cars and trucks.

Clinton said at a rally Monday in Graham, N.C., that she would introduce legislation to impose a windfall profits tax on oil companies and use the revenue to temporarily suspend the gasoline tax.

“At the heart of my approach is a simple belief,” Clinton said. “Middle-class families are paying too much and oil companies aren’t paying their fair share to help us solve the problems at the pump.”

The split occurred as Clinton and Obama were competing intensely in primaries in Indiana and North Carolina, where voters go to the polls May 6. Opinion surveys have shown that the faltering economy and high gas prices are the top concerns of voters across the country.

Clinton said the tax on the oil companies, which have been reporting record profits as oil prices soar to unprecedented levels, would cover all of the lost revenue from the federal tax on gasoline and diesel fuel. She also said no highway projects would suffer.

Obama derided the McCain-Clinton idea of a federal tax holiday as a “short-term, quick-fix” proposal that would do more harm than good, and said the money, which is earmarked for the federal highway trust fund, is badly needed to maintain the nation’s roads and bridges.

The debate erupted as both candidates rounded up more superdelegate endorsements on Monday, with Obama highlighting the backing of Sen. Jeff Bingaman of New Mexico, who is the chairman of the Senate Energy and Natural Resources Committee, while Gov. Michael Easley of North Carolina was preparing to endorse Clinton today.

The split on the gas tax is a relatively rare one for Clinton and Obama, who agree on the broad outlines of policy in most areas. They have both called for the suspension of purchases for the national strategic petroleum stockpile, a supply of oil to protect the country against sudden supply disruptions; new taxes on the oil companies; measures to curb global warming; and heavy federal spending on renewable energy sources. They also have called for a federal investigation of possible manipulation in oil markets.